1. Field of the Invention
This invention relates to fluid absorbent polymer compositions having the capability to absorb large volumes of aqueous fluids rapidly and efficiently.
2. Related Art
Various attempts have been made to produce fluid absorbent polymer compositions that have a high rate of fluid uptake or absorbency. Compositions possessing a high absorbency rate are desired for use in diapers, sanitary napkins and particularly in adult incontinent devices where a large amount of urine must be absorbed rapidly in order to avoid leakage and/or an unpleasant wetness.
One such attempt is reported in U.S. Pat. No. 4,734,478 where fluid absorbent polymer particles are covalently surface crosslinked with a solution containing 0.001 to 10 parts by weight of a polyhydric alcohol, 0.01 to 80 parts by weight of a hydrophillic organic solvent and 0 to 8 parts by weight of water per 100 parts of absorbent polymer and heating the mixture at a temperature of at least 90.degree. C. to react the fluid absorbent polymer with the polyhydric alcohol. This patent also discloses the use of high-speed or high intensity mixers to effect mixing of the polymer particles with the polyhydric alcohol which results in the agglomeration of the wetted polymer particles. The addition of finely divided silica to the covalently surface crosslinked absorbent polymer is also disclosed. The addition of finely divided silica and other inorganic materials to water absorbent polymers is also disclosed in various other U.S. Patents; see for example, U.S. Pat. Nos. 4,286,082 (added after crosslinking), 4,587,308 (added during crosslinking), and 4,500,670 (synthetic silicate and other inorganic powders to increase gel strength).
The surface crosslinking of fluid absorbent polymers is disclosed in U.S. Pat. Nos. 4,043,952 and 4,295,987. The '952 patent discloses conducting the surface crosslinking using a organic liquid or a mixture of an organic liquid and water as the dispersing medium. The '987 patent teaches the use of a divalent ionic crosslinker.
It is the object of this invention to provide a fluid absorbent polymer composition that absorbs water and aqueous ionic fluids at a high absorbency rate. This object is accomplished by the surface crosslinking with an ionic crosslinker and agglomeration of a base absorbent polymer having a fine particle size distribution into larger particles. In the following description of the invention surface crosslinking and crosslinker (in the context of the invention) means ionic surface crosslinking or an ionic crosslinker.